Sounds to me like you ARE being taken advantage of...and mostly because you are one of the few who follows the rules. If the rule is to find your own replacement, and you do so, then there is no reason for management to harrass you by phone or make a personal appearance!

If you don't state your case to your immediate superior then you can't expect anything to change. If you do bring your concerns of infringing on your personal time and how difficult the shift changes are on your health and you get no satisfaction, or worse they make conditions even harder for you in retaliation, then you have to go higher up and talk to HR or even the owner of the company!

Get all your ducks in a row and take control of your working conditions. If you've been a model employee and your bosses take advantage of that dedication while dismissing other employee's slacking...you are setting yourself up as the jackass (meant literally and figuritively) who will carry the largest burden! Even a donkey will kick or stand it's ground when it doesn't like the burden put upon it.

Don't go in angry but DO go in and state your case! If they don't know what you are thinking and feeling then they'll keep loading you up till you break down!

__________________
Minds are like parachutes. They only work when they are open.

~Thomas Dewar~